Caption: The membrane attack complex is one of the methods used by the immune system to attack threats to the body. Compliment dependent cytotoxicity activates the membrane attack complex (MAC) which causes the malignant cell to leak or explode. The C1Q complex consisting of C1Q (blue and green) with serine proteases consisting of dimers of C1r (purple) and C1s (orange) attaches to immunoglobin antibodies which have been attracted by numerous antigens on the surface of the malignant cell. This sequence activates the membrane attack complex which forms pores in the cell membrane. Labelled illustration.